41 replies to this topic

[Nev]

It's a nasty weakness in the car for sure. Not only for track day users, I would imagine a rear wheel hitting a curb could cause this too. Certainly worth owners checking for when they are next under their cars...

[The Batman]

Has the car been in a bump? I imagine this is why it has damage like this rather than track abuse imo

[Rosssco]

Not quite the same (impact related, not fatigue), but when I pranged / crashed a previous VX (subsequently replaced the whole subframe) by hitting the rear wheel side on with a kerb, the tie-rod, wishbone and everything was totally fine - it was the lower suspension 'tower' that deformed.

 

Whether this is a inherent weakness, or deliberate design, its no surprise subframes are in demand..

[Exmantaa]

That's exactly where a Turbo subframe is reinforced by thicker metal plates...

[Nev]

I'd imagine the towers can suffer from both fatigue and curb hits myself.

 

I remember observing the rear subframe when I was lowering/lifting my engine out of the car and it sagged a hell of a lot. I was quite started, perhaps 1 to 2 inches, which is unexpected, as you'd imagine it to be solid.

 

[hairy]

Holy sh!t

[Spitfire Engineering]

Maybe one should put up som FAQ about Yokos and the VX, how the probs look and their cure (if there is any).
 

[*]rear subframe fatigue cracks
[*]hub bolts snapping
[*]rear toe-links bending
[*]more?
[/list]Also quoting Ricky 2772:

"btw, I replaced the 2 bolts holding the hub and shims in place with stonger ones, rated 12.0, instead of the stock 8.0 ones...having experienced the sudden breakdown on one of them while at 120kmh, it was not fun....
....so I decided to upgrade to a stronger alloy... now I feel better when pushing hard... "

 

 

 

 

Quite a few points to discuss here...

 

SUBFRAME

First the stress cracking on the subframe, it is a known weakness though not exactly common. The two obvious advanced solutions are to either:

 

1.  Strengthen the area with additional material usually in the form of a convoluted bracket, this is easier on a new subframe as the base material is perfect, however you need to be careful where you are sending the forces as by stiffening in this manner you are increasing the loading somewhere else and this may not be so visible and maybe not so frangible.

I don't know anyone who has done advanced analysis of a modified subframe so there is an element of extrapolation of data of the possible consequences of the bracket design on the rest of the subframe. If you very carefully checked the later subframes for material thickness and design and copy that you should be reasonably safe.

 

2. You can remove some of the forces on the loaded side (outer during cornering) by fitting a brace across the rear, this shares the applied forces across to both sides of the subframe effectively halving them. In some ways this a better solution for several reasons.

 

A. It is clear how the brace resists lateral forces and if allowed to freely articulate in the other two planes (vertical/longitudinal) via a bearing mount you cannot be loading the subframe anywhere else nor twisting the brace mounting sections of the subframe, so it's a one dimensional solution to a mostly one dimensional problem (this is not strictly true but this is not the place for small percentage considerations)

B. it is very easy and safe to fit, and can be removed/adjusted easily as well.

C. it has a very clear effect on the handling insomuch as it stiffens the rear without giving any secondary negative effects.

 

The brace should be fastened over a large surface area of the subframe to avoid mounting point damage, luckily such a mount is already in place for those with double shear brackets for the toe links as the bracket is perfect for this requirement. Even better, the forces to be considered are coming up through the toe link and the wishbone which share the same bolt as the brace so you are not transferring all of the forces through the subframe but via the common bolt.

All our brace mounting options have always been via a bearing mount so as to maintain the single dimension operation.

The VX specific problem is that it was not designed for a brace so no route across the back of the subframe was designed in, It does fit most cars but there are problems when large bore exhausts are fitted. We do have guide which allows you to check this before committing to purchase one. A new all aluminium brace will be available early next year.

 

 

UPPER PLINTH BOLTS

Lotus made it quite clear and have bulletin for these so there is no need to guess.

The requirement for track cars it raise the specification of the bolts from 8.8 to 10.9

Don't use 12.9 as firstly they are too brittle, and secondly you may damage the thread of the upright with the higher torque, especially if you use the shorter bolts as incorrectly supplied by a popular Lotus dealer.

If you need these we have doing the complete 8 bolt kits for some time very reasonably as a service. No, they are not cheap bolts they are the same certified ones we use for the toe link kits, plated and checked for embrittlement in the UK, we just don't put a large margin on them and when bought with a kit are basically at cost. £9.50 (which includes first class and vat) or £4+vat with a kit.

 

REAR TOE LINKS BENDING

Is this an OE one? 

I have seen an aftermarket one bent in the centre while still attached at both ends and little other damage on the car which begs the question "so how is it uprated then?"

 

[Spitfire Engineering]

Edited by Spitfire Engineering, 26 November 2017 - 11:33 AM.

[JG]

TLDR, what's the short version?

[Foxy]

TLDR, what's the short version?

IRTA: Because Lotus

[Spitfire Engineering]

TLDR, what's the short version?

 

That was the short version

 

OK,

Subframe  = Try prevention it's easier and cheaper the a cure.

HCB's = Just follow the Lotus bulletin.

Toe Links = Get good ones and they don't bend

 

That was easy

[JG]

lovely

[CHILL Gone DUTCH]

i still think i would rather bend a track rod rather the crack the subframe 

[Spitfire Engineering]

i still think i would rather bend a track rod rather the crack the subframe 

 

Not that the two are mutually exclusive or that it can be arranged that you will have a choice unless you deliberately weaken the toe link to ensure this always happens. That would also mean weakening the OE links as if they did not have enough problems ..... However others perhaps would rather risk a cracked subframe than end up sideways into the Armco at 130mph, each to their own I guess    

 

In any case a bent arm is unacceptable as it should be at least as strong as the fasteners as these are the calculated fail points as per the OE setup, the resultant damage/injury due to failed links are well documented and plentiful, not so with a cracked subframe at least I am not aware of any off's due to this??

 

To be clear considering the age, corrosion and fatigue life it is not possible to say at such and such a G, or an impact of such a force over so many milliseconds will do XYZ damage to any particular subframe, it will vary greatly.

 

[cucharillas]

video from Sunday @ Calafat track.

there are many bumpy kerbs on these track. 37 laps x 17 kerbs/lap = 627 kerbs in total.

 

Result:

Missed bolt of reinforced toe link.

 

 

Pics on my Instagram: mister_cucharillas.

Can´t upload on the forum

[Spitfire Engineering]

Pics please?

 

[CocoPops]

Bloody hell, was there a kerb on the track that you didn’t abuse?!

[siztenboots]

Pics please?

 

 

 

https://www.instagra.../p/BqnN7v6gN-t/

 

right rear

[Spitfire Engineering]

 

Pics please?

 

 

 

https://www.instagra.../p/BqnN7v6gN-t/

 

right rear

 

 

Ta, I was trying to get some images of the failed components and the area around it.  

[cucharillas]

Bloody hell, was there a kerb on the track that you didn’t abuse?!

 

 

jajaja nope, there are many seconds on these kerbs.

Full lap its on youtube